1. Field of the Invention
This invention generally relates to a crossed roller bearing assembly, and, in particular, to a spacer for use in such a crossed roller bearing assembly.
2. Description of the Prior Art
A crossed roller rolling contact bearing assembly is well known in the art, and it includes a pair of moving members which move relative to each other and which are formed with guide grooves to define a guide channel in which a plurality of rollers are provided in a crossed arrangement. The guide channel is typically defined in the form of an endless loop. In such a crossed roller bearing assembly, any two adjacent rollers are disposed in a crossed arrangement so that the axis of one of the rollers extends in a direction perpendicular to the axis of each of the two adjacent rollers on both sides when viewed in a longitudinal direction of a guide channel in which the rollers are provided. Since two adjacent rollers are in a crossed arrangement, they are rather unstable in motion so that it has been proposed to provide a spacer between two such adjacent rollers to provide stability to the motion of each of the rollers. Such a spacer for use in a crossed roller bearing assembly is, for example, disclosed in Japanese Patent Post-examination Publication No. 60-25653, Japanese Utility Model Laid-open Publication No. 59-1928 and U.S. Pat. No. 4,479,683.
The prior art spacers proposed, for example, in the above-mentioned patents for use in a crossed roller rolling contact bearing assembly typically have such overall outer shapes as square pillars, cylinders and discs. The prior art spacers are typically so structured to fill almost all of the space defined between two adjacent rollers. Such a prior art structure is advantageous from the viewpoint of providing an increased stability to each of the rollers; however, it also presented several disadvantages, such as an increased sliding resistance and difficulty in maintaining a lubricant, in particular grease of high viscosity, on the guide grooves along which the rollers roll. For this reason, there tended to occur a lubricant scarce condition during operation and in the worst case the bearing could be burned out or frozen in a short period of time.